Base of a roof vent



FIG. 1 is a right side elevational view of a base of a roof vent showing our new design, the left side being a mirror image of the right side shown;

FIG. 2 is a front elevational view thereof;

FIG. 3 is a rear elevational view thereof;

FIG. 4 is a bottom plan view thereof; and

FIG. 5 is a top plan view thereof. 

The ornamental design for a base of a roof vent, as shown and described. 